The present invention relates generally to satellite communication systems, and more particularly to a time division multiple access (TDMA) beacon for satellite system synchronization.
Satellites and other spacecraft are in widespread use for various purposes including scientific research and communications. These scientific and communications missions, however, cannot be accurately fulfilled without uploading and downloading electronic data. In many applications, the satellite relies upon uploading and downloading electronic data for position correction or system diagnostics. In other applications, the satellite acts as a relay to transfer data between two remote points on the Earth. Without the capability to receive and transmit electronic data, proper satellite function is hindered and at times impossible.
Many modem spacecraft act as relays to transfer data between two or more points on the Earth. There are several types of electronic data that these satellites broadcast. These include timing beacon synchronization data, multi-cast/broadcast data service, calibration data, and point-to-point data service. Unfortunately, typical satellites require separate antennas and the electronics required for each antenna for each of the above functions.
For example, a satellite beacon signal is required by a terminal to synchronize time for a TDMA satellite communications system. The beacon signal typically has its own waveform and is generated independent of data transmissions. To conserve satellite power, the beacon is allocated relatively low EIRP. To conserve spectrum, the beacon occupies a small fraction of the downlink bandwidth. To minimize interference with the main data transmission, the beacon is usually located at the edge of the allocated band.
In addition to the added complexity in the generation and recovery of the beacon signal, the conventional approach has a number of inherent problems. First, there is a concern with possible interference from the main data transmission. Second, a small bandwidth can limit the timing accuracy of the beacon. Finally, the timing biases between the data transmission and the beacon signal due to different hardware paths typically need to be calibrated and eliminated.
The disadvantages associated with these conventional satellite system synchronization techniques have made it apparent that a new technique for satellite system synchronization is needed. The new technique should reduce complexity in the generation and recovery of the beacon signal and should not create interference with main data transmission. Additionally, the new technique should have higher timing beacon accuracy, while eliminating timing biases between the data transmission and the beacon signal. The present invention is directed to these ends.
It is, therefore, an object of the invention to provide an improved and reliable TDMA beacon for satellite system synchronization. Another object of the invention is to reduce complexity in the generation and recovery of the beacon signal. An additional object of the invention is to eliminate inference with main data transmission.
In accordance with the objects of this invention, a TDMA beacon for satellite system synchronization is provided. In one embodiment of the invention, a TDMA beacon for satellite system synchronization includes a beacon signal generator and a time division multiplexed switch. The beacon signal generator generates a beacon signal. The TDM switch is coupled to the beacon signal generator and receives the beacon signal. The TDM switch embeds the beacon signal with a data signal into a TDMA signal. The TDMA signal is then broadcast to a ground station where the beacon signal may be extracted from the TDMA signal and used to synchronize a terminal with the satellite system.
The present invention thus achieves an improved TDMA beacon for satellite system synchronization. The present invention is advantageous in that it allows higher timing beacon accuracy, while eliminating timing biases between the data transmission and the beacon signal
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.